Update arg parsing to clap v3

[tranzystorekk]

Slightly breaking change: trailing arguments are now marked as last i.e. they have to be put after a -- marker, which seems to be more manageable/reasonable.

[djc]

Thanks for working on this! In order to make this easy to review, I'd like to have just the minimal changes required to get it compiling with clap, and then have a follow-up PR (or follow-up commits in this PR) to further improve the command-line parsing.

Also could you please elaborate with some examples on things that are now allowed or are no longer allowed with regards to the argument parsing?

[djc]

Why spell out the value_name here?

[tranzystorekk]

It describes what we're actually specifying, i.e. the target shell, otherwise clap just copies the field name

[djc]

Is reordering necessary here or just a style tweak?

[tranzystorekk]

The latter

[tranzystorekk]

Thank you for having me! 😄

As for the new things, clap 3 mostly just cleans up all the APIs and incorporates old structopt under the derive umbrella.

Among the more interesting new additions is the ArgEnum trait which simplifies using enums as arguments, e.g.:

use clap::ArgEnum;

#[derive(ArgEnum)]
enum ProcessingMode {
    Batch,
    Interactive,
}

#[derive(Parser)]
struct Cli {
    #[long, arg_enum]
    mode: ProcessingMode,
}

This would accept args like myprogram --mode batch without any manual impls like FromStr, as well as display possible variants in the help message. The variant names can also be switched similarly to serde, to lowercase, snake_case, kebab-case etc.

[tranzystorekk]

I went ahead and disabled the CLI portion of inferno since it introduced unused clap 2 dependency

[tranzystorekk]

Also could you please elaborate with some examples on things that are now allowed or are no longer allowed with regards to the argument parsing?

I seem to have missed the point of your question, I'm assuming you were asking about the breaking changes I introduced.

Now that the trailing_arguments in both flamegraph and cargo_flamegraph are marked as last, they must be placed after the --, e.g.:

cargo flamegraph -F 10000 -- --my --args -a -b -c

This is slightly more restrictive, but also now the user unambiguously knows how to pass any arguments to their own application.

[djc]

Thanks!